Lead scientist Dr Nir Barzilai said: “The advantage of finding a gene that involves longevity is we can develop a drug that will imitate what this gene is doing. If we can imitate that, then long life can be terrific.”

Professor
Judith Phillips, president of the British Society of Geron­tology, said
the discovery would change how people look at growing old.

She
said: “It’s a huge opportunity because the ageing population is growing
anyway. They would be a huge resource because people would be able to
work longer and they would have a healthier life, and it would
r­evolutionise the way we look at older people.

“And it would reduce costs in terms of care.”

A US study looked at 500 Ashkenazi Jews living in New York with an ­average age of 100.

They
were chosen after previous studies found the group to have a very
specific genetic footprint because their bloodline had been kept very
pure.

Although a third were obese or had
smoked two packets of cigarettes a day for more than 40 years, they
shared three “super-genes” that extended life expectancy.

Two
genes produced “good” cholesterol, which reduced the risk of heart
disease and strokes, while a third gene protected against diabetes.

Those
with the longevity genes had a one in 500 chance of reaching 100,
compared with a one in 10,000 chance in the rest of the population.

Dr
Barzilai, from the Albert Einstein College of Medicine in New York,
said: “Because our centenarians have ­longevity genes, they are
protected against many effects of the environment.

“That’s why they do whatever they want to do and they get through anyhow.”

He
said two of the genes “increase good cholesterol in a ­significant
way”. He added: “There’s no drug that does it so effectively.”

The
specific genotype that seemed to protect against diabetes also appeared
to radically cut that person’s chances of developing Alzheimer’s.

Professor
Jeremy Pearson, associate medical director at the British Heart
Foundation, said: “I think it’s optimistic to say we’re going to have
pills in three years but it would certainly add ­significantly to the
ways in which we can help ­prolong life.

“It’s
perfectly logical that if you have heart disease, you’re likely to live
less long so if you stop that happening, you might live longer.”

The study features on Horizon’s Don’t Grow Old, on BBC2 tonight at 9pm.